Any patient who is to be given a general anesthetic for a surgical procedure is intubated prior to surgery. The anesthetic effectively pharmacologically suppresses brainstem function, inluding a variety of involuntary physiological responses, not the least of which is the ability to cough and clear the upper airway. These brainstem reflexes are suppressed until the anesthetic wears off. Because the tubing that has been inserted into the patient's airway tends to act like a wick--drawing fluid (e.g., secreted saliva) that may be present in the patient's mouth into the patient's airway and lungs--it is critical that the patient's involuntary cough reflex be fully functional at the time the patient is extubated.
Unfortunately, there is currently no mechanism for accurately determining whether or not the patient's ability to involuntarily clear the airway has been fully restored. Instead, because each patient's anesthesia recovery time is different, the standard medical practice is to have a skilled medical practitioner (e.g., anesthesiologist) observe the patient, and then make an `educated guess` that the patient's anesthetic state has completely subsided, and that it is `reasonably safe` to extubate the patient, and allow the patient to receive fluids and/or nutrients by mouth. If the patient's involuntary cough reflex is not yet fully restored, however, the patient is at considerable risk of developing pneumonia, as a result of entry into the airway from the patient's mouth of what would otherwise be expelled secretion and/or foreign matter that could be a substrate for breeding bacteria.
In addition, even in those cases where a patient has the ability to cough both involuntarily and voluntarily, the condition of the patient (for example in the case of coronary bypass surgery) may be such that it is extremely difficult and/or painful to have the patient cough voluntarily to clear and expel secretions, mucous and the like from the patient's airway.